1. Field of the Invention
The present invention relates to a vehicle which is propelled by an electric motor mounted on the vehicle.
2. Description of the Related Art
One type of vehicles which are propelled by an electric motor mounted thereon is a fuel cell vehicle using a solid polymer electrolyte fuel cell. The solid polymer electrolyte fuel cell has a membrane electrode assembly comprising an anode electrode and a cathode electrode and an electrolyte membrane interposed between the electrodes. The electrolyte membrane comprises a solid polymer ion exchange membrane (proton ion exchange membrane). The membrane electrode assembly is sandwiched between separators.
Usually, membrane electrode assemblies and separators are alternately stacked to assemble fuel cells as a fuel cell stack. When a fuel gas, e.g., a hydrogen-containing gas, supplied to each of the anode electrodes of the fuel cell stack, the hydrogen in the gas is ionized on the electrode catalyst and moves through the electrolyte membrane, which is humidified to a suitable level, to the cathode electrode. Electrons produced while the hydrogen is in motion are supplied to an external circuit, which uses the electrons as an electric energy in the form of a direct current.
Since the cathode electrode is supplied with an oxygen-containing gas such as air, hydrogen ions, electrons, and the oxygen gas react with each other on the cathode electrode, producing water.
Fuel cell vehicles employ a fuel cell system which incorporates the above fuel cell stack. As shown in FIG. 25 of the accompanying drawings, a conventional fuel cell system 1 has a fuel cell stack (electric energy supply mechanism) 2 connected to a fuel gas supply unit 3 for supplying a fuel gas such as a hydrogen-containing gas, a coolant fluid supply unit 4 for supplying a coolant fluid, and an oxygen-containing gas supply unit 5 for supplying an oxygen-containing gas such as air.
The fuel gas supply unit 3 has a fuel gas pump (reactant gas supply pump) 6 which is connected to a fuel gas passage (not shown) in the fuel cell stack 2 by a fuel gas supply passage 7. The fuel gas supply unit 3 also has an electric motor 8 coupled to the fuel gas pump 6.
The coolant fluid supply unit 4 has a coolant fluid pump (coolant fluid supply pump) 9 which is connected to a coolant fluid passage (not shown) in the fuel cell stack 2 by a coolant fluid supply passage 10. The coolant fluid supply unit 4 also has an electric motor 11 coupled to the coolant fluid pump 9.
The oxygen-containing gas supply unit 5 has a supercharger (reactant gas supply pump) 12 which is connected to an oxygen-containing gas passage (not shown) in the fuel cell stack 2 by an oxygen-containing gas supply passage 13. The oxygen-containing gas supply unit 5 also has an electric motor 14 coupled to the supercharger 12.
The fuel cell stack 2 supplies electric energy to a main electric motor 15 which is operatively coupled by a transmission 16 to axles 17 with respective tires 18 mounted thereon. The fuel cell stack 2 also supplies electric energy to the electric motors 8, 11, 14 and an electric motor 20 coupled to an air-conditioning compressor 19.
With the conventional fuel cell system 1, the dedicated electric motors 8, 11, 14 are provided for driving the fuel gas pump 6, the coolant fluid pump 9, and the supercharger 12 which serve as devices for supplying the reactant gases and the coolant fluid, and those electric motors 8, 11, 14 require their own drive units (not shown).
The dedicated electric motor 20 associated with the air-conditioning compressor 19 has to be driven. As a result, the overall energy efficiency and space efficiency of the fuel cell system 1 are considerably lowered, the number of parts used is increased, the fuel cell system 1 is complex in structure, and the manufacturing cost of the fuel cell system 1 is high.
There is known in the art a fuel cell engine having at least one wheel motor for rotating tires and a primary motor for actuating various auxiliary equipment, as disclosed in U.S. Pat. No. 6,223,844, for example.
Usually, a relatively large output power is required to accelerate a vehicle. According to the above known fuel cell engine, therefore, the primary motor is of a large size for imparting a desired drive power to the various auxiliary equipment. Even when the vehicle is operating in a mode in which the fuel cell can be kept in a low output level, such as when the vehicle is in an idling mode, the fuel cell generates an unnecessarily large amount of electric energy because the primary motor produces a large output power. The fuel cell engine is thus not efficient in operation.
Furthermore, when the fuel cell is to be shut off while the vehicle is running, the auxiliary equipment and the air-conditioning system need to be turned off independently by the primary motor. Accordingly, the fuel cell is poor in efficiency.